Population dynamics of Saissetia oleae. II. Life-tables and key-factor analysis

The spatial distribution of motile life stages of the two-spotted spider mite Tetranychus urticae Koch in Kenyan small-scale tomato fields was described by Taylor's power law and an enumerative sampling plan was designed for research purposes. The exponential increase of T. urticae populations during three growing seasons permits the development and use of a simple exponential model for the design of a threshold-based chemical control system. For this purpose, a critical threshold of 440 motile mites per sample unit at the end of the growing season (12 weeks after transplanting) was translated into a proportion of 0.83 infested units in sample 3, i.e. five weeks after transplanting. A sequential binomial sampling plan with respect to the proportion of 0.83, five weeks after transplanting, was designed. The exponential model was extended to account for the influence of weather and host plant species. Model development and parameter estimation were based on three data sets (Kenyan tomato fields, Italian and Californian strawberry fields). The model satisfactorily predicted a positive influence on growth rates by (i) changing the host plant from tomato to strawberry, and (ii) temperature, while a negative effect resulted from (iii) rainfall; both (ii) and (iii) are controlled by temperature-rainfall interactions. In contrast, the estimated parameter values did not satisfactorily describe the expected responses at specific temperature and rainfall values. Nevertheless, the model allowed the rating of host plant species in the field. A fourth data set from Swiss apple orchards was used to test the model, and population build-up on the apple host plant appeared to be higher than on tomatoes but lower than on strawberry.

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Population models for threshold-based control of Tetranychus urticae in small-scale Kenyan tomato fields and for evaluating weather and host plant species effects

Knapp

Sarr

Gilioli

et al. 2006

Exp Appl Acarol

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Key factors and regulation of population of Saissetia oleae (Hom., Coccidae) on olive trees in the region of Magnesia, Greece

Stratopoulou

Kapatos

1998

J Applied Entomology

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Population studies of Suissetiu oleue Olivier were carried out in the region of Magnesia (eastern central Greece) in a heavily infested olive orchard for five consecutive generations (1988/89-1992/93). The aim of the study was to investigate the causes of the outbreak and to evaluate the role of natural enemies on the population dynamics of S. oleue. The performed analysis on the constructed life-tables indicated that mortality of crawlers and mortality during autumn and spring, comprising the action of internal parasitoids (mainly Metuphycus helvolus) and predators (mainly coccinelids), were the main key factors that determined the population changes of S. oleae during the course of the study. Mortalities during autumn and spring were related to population density, with direct density-dependent relationships indicating that these mortalities acted both as key factors and regulating mechanisms. The regulating action was probably due to M . helvolus because the estimates of parasitism during the same periods were also related to population density with the same type of relationship. It was concluded that the outbreak was caused by the reduced action of natural enemies, presumably due to pesticide treatments applied against other olive pests the previous years. However, when their population recovered, they suppressed the pest population again. Therefore, preservation of natural enemies by applying selective control methods against the other olive pests is essential.

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Is the Biological Control of Insects a Natural Phenomenon?

Hawkins

Mills²,

Jervis³

et al. 1999

Oikos

164

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Population dynamics of Saissetia oleae. II. Life-tables and key-factor analysis

Cited by 3 publications

References 4 publications

Population models for threshold-based control of Tetranychus urticae in small-scale Kenyan tomato fields and for evaluating weather and host plant species effects

Population models for threshold-based control of Tetranychus urticae in small-scale Kenyan tomato fields and for evaluating weather and host plant species effects

Key factors and regulation of population of Saissetia oleae (Hom., Coccidae) on olive trees in the region of Magnesia, Greece

Is the Biological Control of Insects a Natural Phenomenon?

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